1. Field of the Invention
The present invention generally relates to an electrical connector, and more particularly to an electrical connector used for high-speed transmission.
2. Description of Related Art
Impedance match and EMI issue are two most important things for signal transmission of electrical connectors. Different kinds of ways are adopted by designers to adjust the impedance of contacts to proper value and improve the EMI effect. To adjust the impedance of contacts to proper value, designers usually adopt the way of changing the dielectric constant around the contacts. To improve the EMI effect, designers usually adopt a conductive shell to cover housing and contacts to depress EMI. These solutions are more important for connectors used in external circumstances. As disclosed by U.S. Pat. Nos. 7,052,321 and 6,758,685, conductive shells are adopted to enclose housings and contacts to improve EMI effect. Particularly, rear walls of the conductive shells each define a cutout at lower ends thereof to expose tail portions of the contacts to be soldered on corresponding PCBs. However, it is right the cutouts cause the leakage of noises which affects the EMI effect. It is desired to have an electrical connector with improved conductive shell to improve EMI effect. On the other hand, CN Patent Nos. 2865042 and 2793964 respectively disclose a housing forming a plurality of aligning slots on rear wall to align tail portions of contacts and adopting a spacer to aligning tail portion of contacts. These proposals mainly for how to align tail portions of contacts, and not mentioned impedance match problem. Therefore, how to control impedance to desired value is another problem needing to be resolved.